Hi Derek, sorry i didn't reply sooner! The majority of designers use what we call "stock" images. These images are purchased royalty free by the designer for a reasonable price. There are a number of stock photo websites offering a wide range of photos starting as little as $.50 per image.
Avizion mentions a good free one above, i recommend paying for the service and my favourite stock photography website is
www.corbis.com. For more sites check out the thread in the "resources" forum.
Hope i have been of some assistance.